Morphology Of Core-shell Particles Research Articles

B-182 Advantage of Core-Shell Particle Morphology Over Fully Porous HPLC Column for the Analysis of Vitamin K Compounds by LC-MS/MS

Abstract Background Vitamin K’s are a group of structurally similar, fat-soluble compounds. There are two natural forms K1 (Phylloquinone) and K2 (Menaquinone), where the later has short and longer chain homologues called Vitamin K2-MK-4 and Vitamin K2-MK-7 respectively. Due to the extremely hydrophobic nature and poor ionization characteristics of these compounds, LC-MS/MS analysis at low concentrations becomes challenging. In this communication we make parallel comparisons of three HPLC columns packed with fully porous and core-shell particles to showcase the superiority of core-shell columns for sensitive detection of vitamin K analytes by LC-MS/MS. Method We compared fully porous (Gemini and Luna, Phenomenex, Torrance, CA) and core-shell (Kinetex EVO, Phenomenex) C18 columns for this study. All columns evaluated were 50 × 2.1 mm with a 5 μm particle size to maintain low back pressure for the viscous organic modifier utilized. Deionized water and a combination of isopropanol and acetonitrile (1:1; v/v) were used as mobile phase A and B respectively for chromatographic separation. An Agilent 1290 Infinity series LC system was employed with a SCIEX 6500 QTRAP mass spectrometer under APCI for MS detection. Analyst software 1.7.2 used for data analysis. Results The LC-MS/MS method had a 4-minute runtime for chromatographic separation of the analytes including 1.5 min of equilibration time. The comparison data revealed the Gemini C18 column shows some higher selectivity and resolution values, whereas both EVO and Luna C18 columns were somewhat comparable. However, the core-shell EVO C18 column displayed much higher efficiency with narrower and compressed peak widths, which dramatically increased the peak height for all 3 analytes exhibiting the highest signal/noise ratio. Conclusion The core-shell Kinetex 5 μm, EVO C18 column with its unique organo-silica grafting shows much higher efficiency and sensitive detection capability for vitamin K analysis by LC-MS/MS compared to that of conventional fully porous silica particles.

Designing Multicomponent Polymer Colloids for Self-Stratifying Films.

Aqueous polymer colloids known as latexes are widely used in coating applications. Multicomponent latexes comprised of two incompatible polymeric species organized into a core-shell particle morphology are a promising system for self-stratifying coatings that spontaneously partition into multiple layers, thereby yielding complex structured coatings requiring only a single application step. Developing new materials for self-stratifying coatings requires a clear understanding of the thermodynamic and kinetic properties governing phase separation and polymeric species transport. In this work, we study phase separation and self-stratification in polymer films based on multicomponent acrylic (shell) and acrylic-silicone (core) latex particles. Our results show that the molecular weight of the shell polymer and heat aging conditions of the film critically determine the underlying transport phenomena, which ultimately controls phase separation in the film. Unentangled shell polymers result in efficient phase separation within hours with heat aging at reasonable temperatures, whereas entangled shell polymers effectively inhibit phase separation even under extensive heat aging conditions over a period of months due to kinetic limitations. Transmission electron microscopy is used to track morphological changes as a function of thermal aging. Interestingly, our results show that the rheological properties of the latex films are highly sensitive to morphology, and linear shear rheology is used to understand morphological changes. Overall, these results highlight the importance of bulk rheology as a simple and effective tool for understanding changes in morphology in multicomponent latex films.

Morphological and Elemental Investigations on Co\u2013Fe\u2013B\u2013O Thin Films Deposited by Pulsed Laser Deposition for Alkaline Water Oxidation: Charge Exchange Efficiency as the Prevailing Factor in Comparison with the Adsorption Process

Mixed transition-metals oxide electrocatalysts have shown huge potential for electrochemical water oxidation due to their earth abundance, low cost and excellent electrocatalytic activity. Here we present Co–Fe–B–O coatings as oxygen evolution catalyst synthesized by Pulsed Laser Deposition (PLD) which provided flexibility to investigate the effect of morphology and structural transformation on the catalytic activity. As an unusual behaviour, nanomorphology of 3D-urchin-like particles assembled with crystallized CoFe2O4 nanowires, acquiring high surface area, displayed inferior performance as compared to core–shell particles with partially crystalline shell containing boron. The best electrochemical activity towards water oxidation in alkaline medium with an overpotential of 315 mV at 10 mA/cm2 along with a Tafel slope of 31.5 mV/dec was recorded with core–shell particle morphology. Systematic comparison with control samples highlighted the role of all the elements, with Co being the active element, boron prevents the complete oxidation of Co to form Co3+ active species (CoOOH), while Fe assists in reducing Co3+ to Co2+ so that these species are regenerated in the successive cycles. Thorough observation of results also indicates that the activity of the active sites play a dominating role in determining the performance of the electrocatalyst over the number of adsorption sites. The synthesized Co–Fe–B–O coatings displayed good stability and recyclability thereby showcasing potential for industrial applications.Graphic

Synthesis and characterization of core-shell nanoparticles and their application in dental resins

The aim of this study was to synthesize acrylic core-shell particles and silica-loaded core-shell hybrid particles through emulsion polymerization. Also this work examined the influence of synthesized nanoparticles loading in a Bis-GMA/TEGDMA resin matrix on some mechanical properties of the dental composite resins. Core-shell particles consisting of polybutyl acrylate (PBA) rubbery core and polymethyl methacrylate (PMMA)/polystyrene (PS) shell were synthesized by seeded emulsion polymerization. For preparing the core-shell hybrid particles, first silica particles with diameters of about 68 nm were synthesized based on the Stöber process. Then the surface of silica particles was treated with ɣ-MPS. Afterwards, polymeric shell was coated on silica nanoparticles through emulsion polymerization. The morphology of core-shell particles was examined by SEM/TEM. Mechanical properties (fracture toughness, flexural strength and flexural modulus) of the photo-cured Bis-GMA/TEGDMA dental resins/composites filled with different mass fractions of synthesized nanoparticles were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. Formation of glassy shell on PBA core in core-shell particles, grafting of ɣ -MPS onto the silica particles and encapsulation of modified silica by polymeric shell in core-shell hybrid particles were confirmed using various analytical techniques. The results of mechanical tests showed that fracture toughness of Bis-GMA/TEGDMA dental resins improved about 35% by the inclusion of 5 wt% silica-loaded core-shell hybrid particles with little effect on flexural strength. This study shows that incorporation of proper amount of hybrid core-shell particles in dental composites can improve their fracture toughness and thus may extend their service life.

Starch nanoparticle incorporation in latex-based adhesives

Starch nanoparticles (SNPs) are chosen as renewable alternatives to partially replace petroleum-based monomers and produce bio-based latexes for adhesive applications. To maintain adhesive performance, SNPs are modified (i.e., via increasing cross-link density, vinyl functionalization, and adjusting hydrophilic/hydrophobic balance) to facilitate their incorporation into the latex particles. The modified SNPs are then polymerized in a semi-batch emulsion polymerization at 60 °C, and yield low viscosity latexes with up to 17 wt% SNP loading and 42 wt% solids. TEM/STEM imaging is performed and reveals the presence of a core-shell particle morphology. This is supported by comparing the adhesive properties of SNP-containing latex films from an in situ preparation vs. a blend of acrylic latex with SNPs. The results suggest that the modified SNPs were largely encapsulated into the latex particles rather than in the aqueous phase or at the latex particle/water interface.

Thermally Stable Metallic Nanoparticles Prepared via Core-Cross-linked Block Copolymer Micellar Nanoreactors.

Thermally stable metallic nanoparticles (MNPs) are highly desirable for the melt processing of polymer nanocomposites. However, due to the high surface energy penalty and decreased melting temperature, MNPs are easy to agglomerate and lose their unique properties if there is no protection or confinement layer. In this work, we report a facile and efficient way to synthesize thermally stable MNPs using core-cross-linked polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) reverse micelles as nanoreactors. From infrared results, gold, silver, and palladium ions exhibited distinctive coordination to the 4VP groups with varying chelation strengths. Compared to the non-cross-linked micelles, 1,4-dibromobutane (DBB)-cross-linking of the P4VP cores provided several advantages. First, it prevented severe swelling of the P4VP cores caused by the reducing agents and subsequent merger of swollen micelles. Second, the quaternized P4VP with hydrophilicity enhanced the uptake speed of precursor metal ions into the cores. Third, the cross-linked cores greatly stabilized the MNPs against the high-temperature environment (e.g., 110 °C for 40 h in toluene). In addition, the solubility of the reducing agents also played an important role. Anhydrous hydrazine could swell the P4VP cores and concentric core-shell particle morphology was obtained. On the contrary, triethylsilane could not swell the P4VP cores and thus eccentric core-shell particle morphology was observed. Only the concentric core-shell MNPs exhibited good thermal stability, whereas the eccentric core-shell MNPs did not. This work suggested that these thermally stable MNPs could be good candidates for the melt processing of functional polymer nanocomposites.

Preparation and Properties of Core-Shell Particles Filled β-Nucleated Polypropylene Random Copolymer Composites

To provide polypropylene random copolymer (PPR) with excellent toughness without lowering its rigidity, a novel kind of core-shell particles (CSP) and β nucleating agent (β-NA) were incorporated into PPR by melt blending. The CSP, in which nano-CaCO3 acted as the core and polyethylene (PE) formed the shell, was also prepared through melt blending. The effects of different proportion of PE shell and nano-CaCO3 core on the properties of β-modified PPR composites were investigated. The dispersion and morphology of CSP were studied by transmission electron microscopy (TEM) and the results showed that the CSP dispersed fairly well in the PPR matrix and the core-shell structure was successfully formed. The nano-CaCO3 core was completely encapsulated by PE, especially at the 50/50 weight ratio. The crystallization behaviour of the PPR composites was characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). All the results showed that the relative content of β-form crystal was greatly enhanced with the incorporation of β-NA. Furthermore, the weight ratio change of PE/nano-CaCO3 could also increase the relative content of the β-form crystal. Under the combined effects of β-modification and CSP, the mechanical properties of the PPR composites were greatly enhanced without reducing its rigidity.

Morphology and free volume of nanocomposite Teflon AF 2400 films and their relationship to transport behavior

Free volume is a key property regulating penetrant (gas phase) or solute (solution phase) permeability in polymeric membranes. Thus, we investigated the origins of free volume in two types of Teflon AF 2400 nanocomposites. In nanocomposites from glassy Teflon AF and fluorophilic, solid silica nanospheres, the soft matrix shows exceptionally high apparent fractional free volume (aFFVP)—reaching over 50% at high particle loading. Adding the higher density FNPs to polymer films actually decreases film density. Nanocomposites from plasticized Teflon AF show similarly high aFFV at high particle loading. However, the nano-scale morphologies of the films are very different. The nanocomposites with glassy polymer exist as a polymer matrix with entrained particles. At higher FNP loadings, where the characteristic distance between particles is smaller than the radius of gyration of the polymer, the polymer exists as a vine-like network entraining the particles. Nanocomposite films with plasticized polymer have a packed, core–shell particle morphology with FNPs as the core and plasticized Teflon AF as the eight-nm shell. While the aFFVPs of the two types of films at high FNP loading are similar, systematic studies reveal different mechanisms for the formation of the apparent free volume elements. Distinctive free volume properties lead to remarkably different transport behavior.

Formation of Hollow Polymeric Microspheres with Functionalized Surface on the Basis of Latex Particles with Multilayered Structure

AbstractSummary: Latices with “core‐shell” particle morphology containing polar “core” and a shell on the basis of copolymer of styrene and functional vinyl monomer (allyl alcohol, vinyl acetate, methacrylic acid) has been obtained as a result of graft‐copolymerization initiated from the surface of (meth)acrylate latex particles previously modified with functional polyperoxides. The processes of functional shell grafting as well as the processes of latex particle swelling with obtaining hollow microspheres due to neutralization of core carboxylic groups have been studied.

Preparation of Reactive Composite Latexes by ‘Living’ Radical Polymerization Using the RAFT Process. A New Class of Polymer Materials

A new class of polymer (nanocomposite) materials of di- and triblock polymers of polystyrene, poly(butyl acrylate) and poly(acetoacetoxyethyl methacrylate) with a core-shell particle morphology and a controlled molecular weight distribution were prepared via emulsion polymerization in the presence of a reversible addition/fragmentation chain transfer agent. The film properties of these blocks are far superior to the conventional blend of the two polymers even after crosslinking with 1,6-hexadiamine.